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A stabilized upwind finite-element model is developed to solve the three-dimensional incompressible steady Navier-Stokes equations. The test function is constructed to have a larger weight on the upstream side. This has been achieved by adding a stabilized term to the shape function so as to optimize the numerical wavenumber for convection terms. To avoid Lanczos or pivoting breakdown while solving the resulting unsymmetric and indefinite mixed finite-element matrix equations iteratively, the finite-element equation has been modified by pre-multiplying it with its transpose. The resulting normalized matrix equation becomes symmetric and positive-definite. We can therefore apply a computationally efficient conjugate gradient Krylov iterative solver to get an unconditionally convergent solution. However, the condition number of the new system becomes the square of the original unsymmetric indefinite system. To fully exploit excellent convergence nature of the conjugate gradient iterative solver, an element-by-element strategy is adopted to avoid assembling of all the stiffness matrices obtained at element level. We alleviate the drawback of slower convergence of the conjugate gradient method due to the increased condition number by preconditioning the positive-definite matrix. The resulting preconditioned matrix equation is solved in a matrix-free manner using the preconditioned conjugate gradient iterative solver. The developed finite-element code is first verified by solving a problem amenable to analytical solution. The benchmark lid-driven cavity problem is also solved in a cube for assessing the three chosen iterative solvers. [ABSTRACT FROM AUTHOR]

The effect of flow convection is taken into account in the currently developed phase-field model (PFM) for simulating dendritic growth. In previous PFM studies, flow over a stationary object is wrongly predicted since the predicted velocity magnitude near the fluid–solid interface is not negligibly small. To tackle this problem, the Navier-Stokes equations are solved only in the liquid, while zero flow velocity is prescribed in the stationary object. Simulated results are compared with those computed from two previously proposed models to justify the newly proposed phase-field model. [ABSTRACT FROM AUTHOR]

In the current particle method, we propose a new semi-implicit particle method for more effectively solving the incompressible Navier-Stokes equations at a high Reynolds number. Within the Lagrangian framework, the convective terms in the equations of motion are eliminated, without the problem of convective numerical instability. Also, the crosswind diffusion error generated normally in the case of a large angle difference between the velocity vector and the coordinate line disappears. Only the Laplacian operator for the velocity components and the gradient operator for the pressure need to be approximated on the basis of particle interaction through the currently proposed kernel function. As the key to getting better predicted accuracy, the kernel function is derived subject to theoretical constraint conditions. In the conventional moving-particle method, it is almost impossible to get convergent solution at a high Reynolds number. To overcome this simulation difficulty so that the moving-particle method is applicable to a wider range of flow simulations, a new solution algorithm is proposed for solving the elliptic-parabolic set of partial differential equations. In the momentum equations, calculation of the velocity components is carried out in the particle-moving sense. Unlike the traditional moving-particle semi-implicit method, the pressure values are not calculated at the particle locations being advected along the flowfield. After updating the fluid particle locations within the Lagrangian framework, we interpolate the velocities at uniformly distributed pressure locations. In the current semi-implicit solution algorithm, pressure is governed by the elliptic differential equation with the source term being contributed entirely to the velocity gradient terms. The distribution of particle locations can become highly nonuniform in cases involving a high Reynolds number and under conditions having an apparently vortical flow. As a result, the elliptic nature of the pressure can be considerably destroyed in the course of Lagrangian motion. To retain the embedded ellipticity in the incompressible viscous flow equations, the Poisson equation adopted for the calculation of pressure is solved in a mathematically more plausible fixed uniform mesh so as to get not only fourth-order accuracy for the pressure but also to enhance ellipticity in the pressure Poisson equation. Moreover, the velocity–pressure coupling can be more enhanced in the semi-implicit solution algorithm. The proposed moving and stationary mixed particle semi-implicit solution algorithm and the particle kernel will be demonstrated to be suitable to simulate high-Reynolds number fluid flows by investigating the lid-driven cavity flow problem at Re = 100 and Re = 1,000. Besides the validation of the proposed semi-implicit particle method in the fixed domain, the broken-dam problem is also solved to demonstrate the ability of accurately capturing the time-evolving free surface using the proposed semi-implicit particle method. [ABSTRACT FROM AUTHOR]

In this article we develop a computationally stable and dispersively accurate convective scheme for the incompressible Navier-Stokes equations predicted in non-staggered grids. To enhance the convective stability and improve the dispersion accuracy, the convective terms are approximated by conducting the dispersion analysis to minimize dispersion relation error and Fourier stability analysis. To validate the proposed third-order-accurate two-dimensional numerical scheme, we solve four problems that are all amenable to exact solutions and the lid-driven cavity problem investigated at high Reynolds numbers. Results with good rates of convergence are obtained for the scalar and Navier-Stokes problems. [ABSTRACT FROM AUTHOR]

We aimed to derive a kernel function that accounts for the interaction among moving particles within the framework of particle method. To predict a computationally more accurate moving particle solution for the Navier-Stokes equations, kernel function is a key to success in the development of interaction model. Since the smoothed quantity of a scalar or a vector at a spatial location is mathematically identical to its collocated value provided that the kernel function is chosen to be the Dirac delta function, our guideline is to derive the kernel function that is closer to the delta function as much as possible. The proposed particle interaction model using the newly developed kernel function will be validated through the two investigated Navier-Stokes problems which have either the semianalytical or the benchmark solutions. [ABSTRACT FROM AUTHOR]

In this article, two three-level methods employing the same prolongation operator are proposed for efficiently solving the incompressible Navier-Stokes equations in a two-grid system. Each method involves solving one smaller system of nonlinear equations in the coarse mesh. The chosen Newton- or Oseen-type linearized momentum equations along with a correction step are solved only once on the fine mesh. Within the three-level framework, the locally analytic prolongation operator needed to bridge the convergent Navier-Stokes solutions obtained at the coarse mesh and the interpolated velocities at the fine mesh is developed to improve the prediction quality. To increase prediction accuracy, the linearized momentum equations are discretized within the alternating direction implicit context using our previously developed nodally exact convection-diffusion-reaction finite-difference scheme. Two proposed three-level methods are rigorously assessed in terms of simulated accuracy, nonlinear convergence rate, and elapsed CPU time. [ABSTRACT FROM AUTHOR]

In this article a scheme which preserves the dispersion relation for convective terms is proposed for solving the two-dimensional incompressible Navier–Stokes equations on nonstaggered grids. For the sake of computational efficiency, the splitting methods of Adams-Bashforth and Adams-Moulton are employed in the predictor and corrector steps, respectively, to render second-order temporal accuracy. For the sake of convective stability and dispersive accuracy, the linearized convective terms present in the predictor and corrector steps at different time steps are approximated by a dispersion relation-preserving (DRP) scheme. The DRP upwinding scheme developed within the 13-point stencil framework is rigorously studied by virtue of dispersion and Fourier stability analyses. To validate the proposed method, we investigate several problems that are amenable to exact solutions. Results with good rates of convergence are obtained for both scalar and Navier–Stokes problems. [ABSTRACT FROM AUTHOR]

The present study aims to develop an effective finite-difference model for solving incompressible Navier-Stokes equations. For the sake of programming simplicity, discretization of equations is made on nonstaggered grids without oscillatory solutions arising from the decoupling of the velocity and pressure fields. For the sake of computational efficiency, both segregated and alternating direction implicit (ADI) solution algorithms are employed to reduce the matrix size and, in turn, the CPU time. For the sake of numerical accuracy, a convection-diffusion-reaction finite-difference scheme is employed to provide nodally exact solutions in each ADI solution step. The convective instability problem is thus eliminated, since each convective term is modeled analytically even in multidimensional cases. The validity of the proposed numerical model is rigorously justified by solving one-and two-dimensional problems, which are amenable to analytical solutions. The simulated solutions for the scalar prototype equation agree well with the exact solutions and provide a very high spatial rate of convergence. The same is true for the simulated results of the Navier-Stokes equations. [ABSTRACT FROM AUTHOR]

This article presents finite-element solutions for incompressible Navier–Stokes equations in velocity–pressure variables. Specific to this study is the inclusion of pressure boundary conditions into the mixed finite-element formulation. To provide an in-depth analysis of the finite-element model, rigorous derivations have been carried out. The justification for applying the finite-element code to simulate this class of flow problems is presented by solving a problem which is amenable to analytical solution and the backward-facing step benchmark problem. In addition, results for blood flow in a carotid artery are presented to show the applicability of the finite-element code to geometrically more complex problems. [ABSTRACT FROM AUTHOR]